Tim Berners-Lee, credited with creating the Web, warns that social-networking sites, efforts to prioritize Web traffic and closed systems such as iTunes threaten the Web's capability to promote free speech and open doors to new scientific discoveries, in an essay published in Scientific American.

"If we, the Web's users, allow these and other trends to proceed unchecked, the Web could be broken into fragmented islands. We could lose the freedom to connect with whichever Web sites we want," he wrote.

He says social-networking sites including Facebook, LinkedIn and Friendster threaten the Web's universality. Such sites assemble data such as users' birthdays, e-mail addresses and likes into databases, reusing the information to provide value-added services. The hitch is that such services are available only within their sites, he said.

"Each site is a silo, walled off from the others. Yes, your site's pages are on the Web, but your data are not. You can access a Web page about a list of people you have created in one site, but you cannot send that list, or items from it, to another site," he notes.

"The more this kind of architecture gains widespread use, the more the Web becomes fragmented, and the less we enjoy a single, universal information space," he said.

Facebook managed to work around Google's change, and in response, Google now warns users that if they export their data to Facebook, they won't be able to get it out.

Such closed worlds are also created when companies such as Apple decide not to use open standards. Berners-Lee gives the example of iTunes, where he says that although songs and videos use open URLs, their addresses begin with the proprietary "itunes:" rather than the open "http." That means users can't make a link to information in iTunes and send it to someone else. "You are no longer on the Web. The iTunes world is centralized and walled off. You are trapped in a single store, rather than being on the open marketplace," Berners-Lee wrote.

The trend toward building smartphone apps, rather than Web apps, leads to similar problems, he said. Material in native apps is "off the Web," meaning that users can't bookmark it or link to it.

Such trends lead to similar scenarios as the walled gardens that were popular in the 1990s, such as AOL, that ultimately proved unsatisfying to users, he said. Those environments, even if they are easy to use, "can never compete in diversity, richness and innovation with the mad, throbbing Web market outside their gates," he wrote.

He also wrote that net neutrality is key to the Web's future. "Debate has risen again in the past year about whether government legislation is needed to protect net neutrality. It is," he wrote.

He sounded baffled by a suggestion from Google and Verizon earlier this year that net neutrality should not apply to mobile phones. "It is also bizarre to imagine that my fundamental right to access the information source of my choice should apply when I am on my WiFi-connected computer at home, but not when I use my cell phone," he wrote.

If the basic principles of the Web are upheld--including support for open standards, making data openly shareable, and net neutrality--the Web promises some "fantastic future capabilities," he said.

Linked data is one example of future promise. Tagging individual pieces of data, within a document for example, would allow applications to read and manipulate more information. That could help scientists, for example, more easily collect all data on a certain subject.

"The goal of the Web is to serve humanity," he wrote. "We build it now so that those who come to it later will be able to create things that we cannot ourselves imagine."